Type IV composite pressure vessels represent the current state-of-the-art for compressed gaseous hydrogen storage in fuel cell electric vehicles. A combination of highly demanding safety regulations and the need for cost competitive solutions make the topic of CPVs particularly challenging. Given the elevated material price of carbon fiber, structural optimality is essential to meet both requirements. Thorough understanding of design parameters and mechanical performance of composite pressure vessels is prerequisite to structural optimality. In this paper we investigate the relation of stacking sequence and circumferential ply drop locations on the mechanical performance of type IV composite pressure vessels subjected with internal pressure. This paper builds on previous studies by the authors, which are enhanced by new numerical and experimental results. An experimental set is used, where for a given layup composition the stacking sequence and the circumferential ply drop locations are varied. The experimental results are complemented by a computationally efficient numerical framework, which is composed by the output of a commercial filament winding software, a self-developed geometry correction algorithm and an automated FE model generation program. The numerical results are compared with outer surface strains obtained by means of three-dimensional digital image correlation, the final burst pressures and the vessel remainders. The achieved burst pressures vary between 152.6 and 188.6MPa, depending on design configuration. For the layup composition in this investigation, the placement of tangentially reinforcing layers (e.g. circumferential and high-angle helical layers) as innermost layers led to overall higher cylinder strengths compared to sequences, where these layers were located as outermost. The retraction of circumferential ply drop locations was found to impact the burst performance differently in dependence of the stacking sequence. For sequences, where circumferential layers were located as outermost, a retraction of ply drop locations by 12mm showed barely any differences in burst pressure (-1.9%). For sequences, where these layers were located as innermost, a severe decrease (-19.1%) was noticed once the ply drop locations were retracted by up to 9mm. The results not only underlined the criticality of both design parameters and their interaction with each other, but also showcased a computationally efficient numerical framework capable of capturing distinct mechanical responses for a variety of layups at least trend-wise.

Commercial development of gaseous hydrogen storage in fuel cell electric vehicles is inevitably subjected to reliable and cost-effective design of composite pressure vessels. In this context, certainty in the design process is sought, which is determined by how well the vessel's mechanical response is understood, but more importantly to which accuracy the final collapse can be predicted. As such, a symbiosis of numerical and experimental work appears as a leading path towards robust design methodologies, where both analyses complement and scrutinize each others validity. This research presents the analysis on the mechanical response of composite pressure vessels during internal pressure loading through the correlation of numerical and experimental results on various degrees of complexity. Based on an extensive experimental dataset, a three-dimensional FE model is implemented on a realistic vessel geometry, evaluating its constitutively elastic behavior, and its response under failure and damage progression. Likewise, an established experimental framework is used to derive data by means of contour scans, outer surface strains, airborne acoustic emissions and final burst pressure. The precise recreation of the vessel geometry, together with the detailed analysis approach, permits to show a reasonable agreement between the predicted and the measured structural responses, the sequence of damage onset, and the final collapse occurring in the cylindrical region (<1%). Discrepancies still exist because of the remaining uncertainty concerning the individual layer geometry and the characterization of damage in the helical plies. Altogether, through the alignment of experimental and numerical analyses, this work provides the base for further optimization frameworks, in which an adequate representation of the vessel's meridional thickness profile and material properties stands out as necessary feat to accurately reproduce the mechanical response and final strength in a time- and cost-effective design process.

The industrialization of fuel cell electric vehicles demands cost efficient storage solutions for hydrogen. While gaseous storage in type IV pressure vessels is currently the most mature technology, further structure optimization needs to be undertaken in order to meet cost requirements. This research investigates the effects of stacking sequence of composite pressure vessels regarding laminate quality, structural deformation and finally burst pressure. Therefore, a known laminate is studied on a subscale vessel geometry with changing stacking sequences. The specimens are pressurized in a specially designed chamber up to burst pressures of 166.11 MPa. Through a multisensor arrangement of stereometric systems, the deformation is tracked up to burst by using 3D digital image correlation. The experimental results show a difference of 67% in burst pressure between the investigated stacking sequences. Experimental cylinder strains and burst pressures are compared to results derived from 3D elasticity theory with implemented first ply failure criterion. Additionally, using X-ray computed tomography and acid digestion tests, insights about the distribution of fiber volume fraction and porosity are provided. For the investigated sequences in this research, the results show the considerable influence of stacking sequence on the laminate quality, the structural deformation and finally the burst pressure of composite pressure vessels. Moreover, it is shown that while the used 3D elasticity approach proved to be a useful tool for the prediction of strains and failure in the cylindrical section, discrepancies between prediction and experiment can arise based on preliminary failure occuring at the cylinder-dome transition. The results therefore emphasize the need for analytical and numerical analysis strategies to consider transition-related effects between cylinder and dome.